Hip dysplasia (human)
|Hip dysplasia (human)|
|Classification and external resources|
Congenital dislocation of the left hip in an elderly person. Closed arrow marks the acetabulum, open arrow the femoral head.
Some sources prefer "developmental dysplasia of the hip" (DDH) to "congenital dislocation of the hip" (CDH), finding the latter term insufficiently flexible in describing the diversity of potential complications.
The use of the word congenital can also imply that the condition already exists at birth. This terminology introduces challenges, because the joint in a newborn is formed from cartilage and is still malleable, making the onset difficult to ascertain.
The term is not used consistently. In pediatric/neonatal orthopedics it is used to describe unstable/dislocatable hips and poorly developed acetabula. For adults it describes hips showing abnormal femur head or acetabular x-rays.
Some sources prefer the term "hip dysplasia" over DDH, considering it to be "simpler and more accurate", partly because of the redundancy created by the use of the terms developmental and dysplasia. TYPES OF DDH include subluxation, dysplasia, and dislocation. The main types are the result of either laxity of the supporting capsule or an abnormal acetabulum.
Forms of the condition
The condition can be bilateral or unilateral:
- If both hip joints are affected one speaks of "bilateral" dysplasia. In this case some diagnostic indicators like asymmetric folds and leg-length inequality do not apply.
- In unilateral dysplasia only one joint shows deformity, the contralateral side may show resulting effects. In the majority of unilateral cases the left hip has the dysplasia.
If the joint is fully dislocated a false acetabulum often forms (often higher up on the pelvis) opposite the dislocated femoral head position.
In actetabular dysplasia the acetabulum (socket) is too shallow or deformed. The center-edge angle is measured as described by Wiberg. In coxa vara the femur head grows at too narrow an angle to the shaft, in coxa valga the angle is too wide.
A rare type, the "Beukes familial hip dysplasia" is found among Afrikaners that are members of the Beukes family. The femur head is flat and irregular. Sufferers develop osteoarthritis at an early age.
In 1979 Dr. John F. Crowe et al. proposed a classification to define the degree of malformation and dislocation. Grouped from least severe Crowe I dysplasia to most severe Crowe IV. This classification is very useful for studying treatment results.
Rather than using the Wiberg angle because it makes it difficult to quantify the degree of dislocation they used 3 key elements to determine the degree of subluxation: A reference line at the lower rim of the "teardrop", junction between the femoral head and neck of the respective joint and the height of the pelvis (vertical measurement). They studied anteroposterior pelvic x-rays and drew horizontal lines through the lower rim of a feature called "teardrop". The distance between this line and the middle lines of the junction between femur head and neck gave them a measure of the degree of femur head subluxation. They further established that a "normal" diameter of the femur head measures 20% of the height of the pelvis. If the middle line of the neck-head junction was more than 10% of the pelvis height above the reference line they considered the joint to be more than 50% dislocated.
The following types resulted:
|Crowe I||Femur and acetabulum show minimal abnormal development.||Less than 50% dislocation|
|Crowe II||The acetabulum shows abnormal development.||50% to 75% dislocation|
|Crowe III||The acetabula is developed without a roof. A false acetabulum develops opposite the dislocated femur head position. The joint is fully dislocated.||75% to 100% dislocation|
|Crowe IV||The acetabulum is insufficiently developed. Since the femur is positioned high up on the pelvis this class is also known as "high hip dislocation".||100% dislocation|
||This section may require cleanup to meet Wikipedia's quality standards. (November 2008)|
Hip dysplasia is considered to be a multifactorial condition. That means that several factors are involved in causing the condition to manifest. Cause is unknown but common in breech position or large fetal size.
A genetic factor is indicated by the trait running in families and increased occurrence in some ethnic populations (e.g. native Americans, Lapps / Sami people). A locus has been described on chromosome 13. Beukes familial dysplasia, on the other hand, was found to map to an 11-cM region on chromosome 4q35. With nonpenetrant carriers not affected.
As an acquired condition it has often been linked to traditions of swaddling infants, use of overly restrictive baby seats, carriers and other methods of transporting babies, or use of a cradle board which locks the hip joint in an "adducted" position (pulling the knees together tends to pull the heads of the femur bone out of the sockets or acetabulae) for extended periods. Modern swaddling techniques have been developed to relieve stress on hip joints caused by traditional swaddling methods.
Further risk factors include breech birth, genetics (family history), and firstborns. In breech position the femoral head tends to get pushed out of the socket. A narrow uterus also facilitates hip joint dislocation during fetal development and birth.
Most countries have standard newborn exams that include a hip joint exam screening for early detection of hip dysplasia. Sometimes during an exam a "click" or more precisely "clunk" in the hip may be detected (although not all clicks indicate hip dysplasia). When a hip click (also known as "clicky hips" in the UK) is detected, the child's hips are tracked with additional screenings to determine if developmental dysplasia of the hip is caused.
The condition can be confirmed by ultrasound and X-ray. Ultrasound imaging yields better results defining the anatomy until the cartilage is ossified. When the infant is around 3 months old a clear roentgenographic image can be achieved. Unfortunately the time the joint gives a good x-ray image is also the point at which nonsurgical treatment methods cease to give good results. In x-ray imaging dislocation may be indicated if the Shenton's line (an arc drawn from the medial aspect of the femoral neck through the superior margin of the obturator foramen) does not result in a smooth arc. However in infants this line can be unreliable as it depends on the rotation of the hip when the image is taken ()
Asymmetrical gluteal folds and an apparent limb-length inequality can further indicate unilateral hip dysplasia. Most vexingly, many newborn hips show a certain ligamentous laxity, on the other hand severely malformed joints can appear stable. That is one reason why follow-up exams and developmental monitoring are important. Frequency and methods of routine screenings in children is still in debate however physical examination of newborns followed by appropriate use of hip ultrasound is widely accepted.
The Harris hip score (developed by William H. Harris MD, an orthopedist from Massachusetts) is one way to evaluate hip function following surgery. Other scoring methods are based on patients' evaluation like e.g. the Oxford hip score, HOOS and WOMAC score. Children's Hospital Oakland Hip Evaluation Scale (CHOHES) is a modification of the Harris hip score that is currently being evaluated.
Hip dysplasia can develop in older age. Adolescents and adults with hip dysplasia may present with hip pain and in some cases hip labral tears. X-rays are used to confirm a diagnosis of hip dysplasia. CT scans and MRI scans are occasionally used too.
Given the very real possibility of a limp, constant and/or debilitating pain, complicated treatment and impaired mobility later in life, careful developmental monitoring and early intervention are indicated. The worst possible consequence of non treatment is developing early arthritis, sometimes even during teenage years. All treatment aims to delay the onset of arthritis, but no treatment is fully successful in avoiding it.
Harnesses, casts, and traction
Early hip dysplasia can often be treated using a Pavlik harness (see photograph) or the Frejka pillow/splint in the first year of life with usually normal results. Complications can occur when using the Pavlik Harness. Cases of Femoral Nerve Palsy and Avascular Necrosis of the femoral head have been reported with the use of the Pavlik harness, but whether these cases were due to improper application of the device or a complication encountered in the course of the disorder remains unresolved. Complications arise mainly because the sheet of the iliopsoas muscle pushes circumflex artery against the neck of the femur and decreases blood flow to the femoral head. That is the reason why the Frejka pillow is not indicated in all the forms of the developmental dysplasia of the hip.
baby wearing a Bock harness
Other devices employed include the spica cast, particularly following surgical closed reduction, open reduction, or osteotomy in babies and young children. Traction is sometimes used in the weeks leading up to a surgery to help stretch ligaments in the hip joint, although its use is controversial and varies amongst physicians.
In older children the adductor and iliopsoas muscles may have to be treated surgically because they adapt to the dislocated joint position (contracture). Braces and splints are often used following either of these methods to continue treatment. Although some children "outgrow" untreated mild hip dysplasia and some forms of untreated dysplasia cause little or no impairment of quality of life, studies have as yet been unable to find a method of predicting outcomes. On the other hand, it has often been documented that starting treatment late leads to complications and ends in poor results.
One avenue of research is using stem cells. They are applied in grafting (bone grafting) or by seeding porous arthroplasty prosthesis with autologous fibroblasts or chondrocyte progenitor cells to assist in firmly anchoring the artificial material in the bone bed.
Hip replacement and osteotomy
Hip dysplasia is often cited as causing osteoarthritis of the hip at a comparatively young age. Dislocated load bearing surfaces lead to increased and unusual wear. Although there are studies that contradict these findings. (see ) Peri-acetabular osteotomy (PAO) surgery can be used to realign the hip joint in some adolescents and adults. Subsequent treatment with total hip arthroplasty (hip replacement) is complicated by a need for revision surgery (replacing the artificial joint) owing to skeletal changes as the body matures, loosening/wear or bone resorption. Hip resurfacing is another option for correcting hip dysplasia in adults. It is a type of hip replacement that preserves more bone, and may work for younger hip dysplasia patients. 
In the television program "ER," Kerry Weaver uses a crutch owing to congenital hip dysplasia. In season 12, she undergoes a hip replacement to cure her dysplasia when her previously untreated joint worsens.
The Frejka Pillow Splint was named after Dr. Bedrich Frejka (1890-1972), a Czech Orthopedic Surgeon. The Pavlik Harness was named after Dr. Arnold Pavlik (1902-1962), also a Czech Orthopedic Surgeon.
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- International Hip Dysplasia Institute (IHDI)
- Online orthopedic textbook 
- Children's Hospital Central California - Developmental Dysplasia of the Hip (DDH)
- United Kingdom Support group for DDH, Clubfoot and other lower limb disorders